Akka in Action, Second Edition by Francisco Lopez-Sancho Abraham;

Author:Francisco Lopez-Sancho Abraham; [Abraham, Francisco López-Sancho]
Language: eng
Format: epub
Publisher: Simon & Schuster
Published: 2023-06-19T22:00:00+00:00

9.3.4 Tagging

When you save to the journal, you usually mark each event so other processes can read the journal by filtering for those marks. After all, the journal is just a table in a database. The tagging is done as follows:

EventSourcedBehavior[Command, Event, State](...) .withTagger( _ => Set("tag1", "tag2")) ❶

❶ Adds these two tags no matter what event

Another typical use case for tagging is to parallelize reading by assigning a set of IDs to a tag so each reader can focus on a particular tag, just like a partition. You can use both in the container to tag specific events and parallelize:

.withTagger{ case event: CargoAdded => Set("container-tag-"+ containerId.toInt % 3, "CargoAdded") ❶ case _ => Set("container-tag-"+ containerId.toInt % 3) ❷ }

❶ Adds these two tags when CargoAdded

❷ Adds only this tag for the rest of the events

These settings allow a maximum parallelism of 3 to read CargoAdded events or the rest of the events as a whole.

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